1. Field of the Invention
This invention is related to fluid control valves and more specifically to corrosion and deposition protected valve apparatus and methods.
2. State of the Prior Art
Valves are used in myriad applications in which corrosive gases or precursors of various kinds have to flow through them. In some applications, for example, in some chemical vapor deposition (CVD) systems, certain valves have to handle different materials that are themselves corrosive and/or reactive and which tend to attack internal metal and other components of valves or which cross-react with each other to deposit solid by-products in the valves and other piping and system components. Such corrosion or solid depositions can shorten valve service lifetimes and cause excessive and expensive shut-downs and repairs in CVD systems.
To avoid or at least minimize such unwanted corrosion and/or deposition, the valves, piping, and other components are often made with stainless steel or other corrosion resistant materials and are heated in order to maintain their temperatures high enough to vaporize any materials that start to condense on their surfaces or to prevent reactions that, at lower temperatures, may form byproducts which would deposit on the surfaces. Some valves, for example isolation valves, which are sometimes used in forelines of CVD systems, i.e., between the CVD reaction chamber and the vacuum pump, use flexible stainless steel bellows to isolate the vacuum in the valve chamber from the atmospheric pressure in the valve actuator apparatus. However, such bellows are generally made of thin stainless steel or other metal in order to be flexible enough to accommodate the reciprocal motion of the valve actuator apparatus as the valve opens and closes, and such thin material, even though it is stainless steel, is vulnerable to chemical attack and corrosion from corrosive gases flowing through the valve chamber. Also, some solid by-products, e.g., silicon dioxide, have high melting temperatures and may not be sublimated. Deposition of such solid materials on the bellows surface generates a significant amount of particles, which not only is a source of unwanted contamination in the CVD system, but can also affect the mechanical strength of the bellows.
To address these problems, the isolation valve in U.S. Pat. No. 8,196,893, which is incorporated herein by reference for all that it discloses, provides a protective cup around the bellows to isolate the bellows from the valve chamber when the valve is open to allow flow of gases through the valve. While that protective cup in U.S. Pat. No. 8,196,893 is generally effective for protecting the bellows in some applications, it does not isolate the bellows from the valve chamber when the valve is closed. Therefore, it would not be effective, for example, to protect the bellows in situations where two or more of the valve actuator and closure apparatus are placed together in a common valve chamber or manifold such that the bellows of a closed valve is exposed to corrosive gases flowing through the common valve chamber or manifold with an open valve.
The foregoing examples of related art and limitations related therewith are intended to be illustrative, but not exclusive or exhaustive, of the subject matter. Other aspects and limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings.